Classes don't conform to protocols adopted through categories without matching implementations

protocol-conformation-experiments

#import <Foundation/Foundation.h>

@protocol ProtocolOne <NSObject>
@optional
- (void)one;
@end

@protocol ProtocolTwo <NSObject>
@optional
- (void)two;
@end

@protocol ProtocolThree <NSObject>
@optional
- (void)three;
@end

@protocol ProtocolFour <NSObject>
@optional
- (void)four;
@end

@interface Test : NSObject <ProtocolOne>
@end

@interface Test () <ProtocolTwo>
@end

@interface Test (CategoryWithMatchingImplementation) <ProtocolThree>
@end

@interface Test (CategoryWithOnlyTheInterface) <ProtocolFour>
@end

@implementation Test
@end

@implementation Test (CategoryWithMatchingImplementation)
@end

int main(int argc, char *argv[]) {
  @autoreleasepool {
    NSLog(@"[Test conformsToProtocol:ProtocolOne]   ? %@", [Test conformsToProtocol:@protocol(ProtocolOne)] ? @"YES" : @"NO");
    NSLog(@"[Test conformsToProtocol:ProtocolTwo]   ? %@", [Test conformsToProtocol:@protocol(ProtocolTwo)] ? @"YES" : @"NO");
    NSLog(@"[Test conformsToProtocol:ProtocolThree] ? %@", [Test conformsToProtocol:@protocol(ProtocolThree)] ? @"YES" : @"NO");
    NSLog(@"[Test conformsToProtocol:ProtocolFour]  ? %@", [Test conformsToProtocol:@protocol(ProtocolFour)] ? @"YES" : @"NO");

//  Output:
//  2015-05-31 22:15:42.612 Untitled 7[1996:53196] [Test conformsToProtocol:ProtocolOne]   ? YES
//  2015-05-31 22:15:42.612 Untitled 7[1996:53196] [Test conformsToProtocol:ProtocolTwo]   ? YES
//  2015-05-31 22:15:42.612 Untitled 7[1996:53196] [Test conformsToProtocol:ProtocolThree] ? YES
//  2015-05-31 22:15:42.612 Untitled 7[1996:53196] [Test conformsToProtocol:ProtocolFour]  ? NO
  }
}